The present invention relates to a rotary machine for a compression or an expansion of a gaseous working fluid.
More particularly, the invention relates to such a machine of the kind comprising a machine housing, a rotor which is rotatably mounted within said housing and which, in its peripheral outer surface, is provided with at least one helically extending groove, having a depth varying along its length and serving as a flow passage for the working fluid, and a separation wheel which is mounted for rotation around a rotary axis, located at a distance from the rotary axis of the rotor and oriented in a direction deviating from the direction of the latter axis, and which comprises a central hub portion and a number of blades, protecting in at least approximately radial directions from said hub portion and evenly distributed in the circumferential direction of said wheel, said blades serving as separation elements, successively insertable into the groove of the rotor and arranged to divide the groove into a number of working chambers which follow one after the other in the longitudinal direction of the groove and which, during coordinated simultaneous rotation of the rotor and the separation wheel, are brought to move along the groove in the longitudinal direction thereof while successively changing their volume.
Machines of the above kind have been known for a very long time. Notwithstanding this fact, they have however not found any appreciable practical use. Most probably, the main reason is that previously one has not managed to avoid that the wheel blades, which serve as separation elements, are subjected to a hard wear, resulting in a rapid deterioration of their ability to separate the working chambers, located at opposite sides of said blades, in a satisfactory manner from each other.
Therefore, an object of the present invention. is to provide an improved rotary machine of the kind initially specified, in which the above-mentioned drawback of the machines previously known can be avoided.
The invention is based on the understanding that the main reason why, in the known machines, the wheel blades are subjected to a rapid wear is that, at their high-pressure sides, they have edge surfaces which, during the operation of the machine, are subjected to the action of the working fluid, which is present at the high-pressure side of the wheel blades and which is under high pressure, and that the wheel blades consequently are brought to bear very heavily against the walls of the rotor groove.
In order to avoid such an unfavourable action on the wheel blades from the pressure of the working fluid and a consequential rapid wear of said blades, according to the invention it is proposed that the wheel blades should have peripheral edge portions, having an acute-angled wedge-shaped profile and terminating into thin sealing edges, moveable along the walls of the groove and located at least approximately flush with the main surfaces of the wheel blades, located at the high-pressure sides of the wheel blades.
By providing the wheel blades with edge portions shaped in the above manner, it is possible easily to avoid that, at the high-pressure sides of the wheel blades, there will exist any edge surfaces which are exposed to the working fluid and upon which said fluid can exert an unfavourable action of the kind above described.
In a manner known per see, the separation wheel may be arranged to be brought to carry out a rotary movement, coordinated to the rotary movement of the rotor, through the action of forces transmitted to the separation wheel from the rotor via the walls of the rotor groove and the wheel blades. Naturally, if the separation wheel is driven in this manner, a certain contact pressure will occur between portions of the walls of the rotor groove and the wheel blades. However, this contact pressure is very low in comparison with the pressure that occurs in previously known machines due to the action of the pressure of the working fluid upon edge surfaces, located at the high-pressure sides of the wheel blades and exposed to said medium, and therefore, it need not cause any appreciable wear of the sealing edges of the wheel blades. Besides, such a wear can easily be counteracted by successively introducing small amounts of a lubricant into the rotor groove, for instance by means of the separation wheel.
However, in order to completely avoid the risk of any wear of the sealing edges of the separation wheel, caused by a contact between portions of the walls of the rotor groove and the wheel blades, the separation wheel may alternatively be arranged to be driven by separate driving means, for instance by an outer transmission, connected between the rotor and the separation wheel and preferably consisting of a cog-belt transmission which is free from backlash.
The wheel blades may have many different shapes. However, according to a preferred embodiment of the invention, they may advantageously have a part-circular shape. This means that the rotor groove may have a corresponding cross-sectional shape which, in practice, is very favourable as it will make it possible to produce the rotor groove in an astonishingly easy way.
The rotor may suitably have a generally frustoconical shape, at least along a substantial portion of its length. Such a shape of the rotor is favourable in several respects.
Furthermore, the separation wheel may preferably have three wheel blades.
Additionally, at their high-pressure sides, the wheel blades may suitably have plane main surfaces which are located in a plane perpendicular to the rotary axis of the separation wheel.
The invention also has for its purpose to provide a favourable new method for producing a rotor for a rotary machine of the kind initially specified.
The method, according to the invention proposed for said purpose, is primarily characterized in that the helically extending groove in the rotor is produced by subjecting a rotor blank to a successive machining along the desired extension length of the groove by means of a cutting or grinding tool which rotates around a rotary axis, oriented in a direction parallel to the intended direction for the rotary axis of the separation wheel, and which has an at least approximately wedge-shaped edge. By producing the rotor groove in this manner, one can make sure that, along its total length, the groove will get a shape very accurately adapted to the shape of the wheel blades, whereby it will be possible to reduce the dimensions of the inevitable leak gaps between the wheel blades and the walls of the groove to a minimum.
When carrying out the above method, the rotor blank may suitably be rotated around the intended rotary axis for the rotor during simultaneous coordinated parallel motion of the rotary axis of the tool relatively to the rotor blank along an arc-shaped path around the intended rotary axis for the separation wheel. If the wheel blades have a part-circular shape and the rotor groove then should have a corresponding cross-sectional shape, any further motion in addition to the above-mentioned parallel motion along a part-circular path need not be imparted to the rotary axis of the tool. However, if the wheel blades have another shape, for instance a part-elliptic shape, it is necessary to impart to the rotary axis of the tool, superimposed on said motion thereof, an additional parallel motion relatively to the rotor blank along an additional path, depending upon the desired cross-sectional shape of the rotor groove. While, in the first-mentioned case, it is possible to use a tool which has an effective radius, corresponding to the desired radius of the contour of the groove, and which constantly acts upon the groove contour along the entire length of said contour, in the last-mentioned case it is necessary to utilize a tool which has a substantially smaller effective radius and which through the superimposed additional parallel motion of the rotary axis of the tool is brought to act on the groove at successive locations along the contour of the groove.
Especially, if the groove is pre-formed in a cast rotor blank, a high surface finish of the groove may be obtained through machining the rotor blank in one single step, for instance by means of a suitable milling tool. However, if required, the groove may instead be produced through machining the rotor blank in at least two consecutive steps, comprising at least one coarse-machining step and at least one subsequent fine-machining step.